Chikage Kamiyashiro grew up within Shumisen, a clandestine organization committed to sealing mononke demons using specialized spirits called "In." His childhood was shattered when traitors within Shumisen murdered his father. This trauma plunged him into emotional withdrawal and isolation. Years later, having mastered the art of wielding "In," he accepted an undercover mission to infiltrate Shumisen and execute the traitors responsible for his father's death. This quest defined his existence, compelling him to confront those whose betrayal fractured both the society and his early life.